Rinse the ginger and then use a spoon to gently scrape off the skin. Slice it very thinly, ideally with a mandolin or vegetable peeler to get the slices extra thin, but a sharp knife will work too. You should have around 1 cup of sliced ginger. Place it in a sterilized jar.
In a small saucepan, stir together the sugar, water, rice vinegar, and salt, so that the sugar dissolves. Bring to a boil over medium high heat and then pour the mixture over the ginger. Let cool slightly and then cover and refrigerate overnight before serving. It will keep in the fridge for up to two weeks.